On optical fiber datalinks, optical noise is typically asymmetrical. In other words, an optical “1” bit typically contains more noise than an optical “0” bit. Thus, after optical-to-electrical conversion, the noise asymmetry results in an eye height of a differential “1” bit that is smaller than an eye height of a differential “0” bit. This may result in a higher bit error rate (BER) for the differential “1” bit as compared to the differential “0” bit. It is desirable to adjust the zero-crossing points of the incoming data in order to balance these eye heights of the differential bits.